Porphyrin Acceptor Research Articles

Push–pull type porphyrin based sensitizers: The effect of donor structure on the light-harvesting ability and photovoltaic performance

Push–pull type porphyrin-based sensitizers have become promising candidates for high-efficiency dye sensitized solar cells (DSCs). It is of importance to understand the fundamental structure-physical property-photovoltaic performance relationships by varying the donor and acceptor moieties. In this work, two new porphyrin-based sensitizers, WW-7 and WW-8, were synthesized and compared with the known sensitizer YD20. All the three dyes have the same porphyrin core and acceptor group (ethynylbenzoic acid) but their donor groups vary from the triphenylamine in YD20 to meso-diphenylaminoanthracene in WW-7 to N-phenyl carbazole in WW-8. Co(II/III)-based DSC device characterizations revealed that WW-7 showed enhanced light harvesting ability in comparison to YD20 with improved incident photon-to-collected electron conversion efficiencies (IPCEs). As a result, WW-7 displayed much higher short circuit current (Jsc: 13.54 mA cm−2) and open-circuit voltage (Voc: 0.829 V), with a power conversion efficiency (η) as high as 7.7%. Under the same conditions, YD20 cell exhibited a power conversion efficiency of 6.6% and the dye WW-8 showed even lower efficiency (η = 4.6%). Detailed physical measurements and theoretic calculations were conducted to understand the difference and reveal how three different donor structures affect their molecular orbital profile, light-harvesting ability, energy level alignment, and eventually the photovoltaic performance.

Spectral Properties of Water-Soluble Conjugated Polymer PFP/DNA/Porphyrin Complex

Photodynamic therapy (PDT) is a particular treatment of tumors, which localizes the biological responses by the way that light is applied. In this paper, we have designed a water-soluble system potentially for PDT, which could selectively generate singlet oxygen efficiently under both of one-and two-photon excitation. This complex consists of a cationic water-soluble conjugated polymer PFP, anionic DNA and a cationic porphyrin. The cationic conjugated polymer PFP and porphyrin are connected by anionic DNA through electrostatic interactions. Energy transfer from conjugated polymer PFP (donor) to porphyrin (acceptor) is available since the considerable overlapping between the emission of donor and the absorption of acceptor (S-0 -> S-2). Steady-state spectra and fluorescence lifetime measurements have been performed on the complex with different DNA sequences in order to achieve the energy transfer efficiency. The results of steady-state fluorescence spectra show that there is a remarkable change of fluorescence intensity of the complex with G-quadruplex DNA, which indicates significant energy transfer from the donor to the acceptor. Furthermore, the greatest change of fluorescence lifetime measured by means of time-correlated single photon counting (TCSPC) also proves the highest energy transfer efficiency of the system with G-quadruplex DNA. Singlet oxygen quantum yield can be obtained by the detection of singlet oxygen emission spectra. Porphyrin bound to G-quadruplex DNA has the highest singlet oxygen quantum yield, which suggests this system a possible application in PDT since singlet oxygen could kill tumor cells. Two-photon absorption cross section has also been measured, which reflects the light-harvesting efficiency of the conjugated polymer PFP. The result shows that the conjugated polymer PFP owns large two-photon absorption cross section in the region of 720 similar to 850 nm where the transmission in tissue is higher compared to the visible light. The energy transfer efficiency and singlet oxygen quantum yield are both selective for different DNA sequences. G-quadruplex DNA that is very rich in tumor cells has the highest selectivity, which makes this system a potential application in PDT.

Synthesis and investigation of donor-porphyrin-acceptor triads with long-lived photo-induced charge-separate states.

Two donor-porphyrin-acceptor triads have been synthesized using a versatile Suzuki-coupling route. This synthetic strategy allows the powerful donor tetraalkylphenylenediamine (TAPD) to be introduced into tetraarylporphyrin-based triads without protection. The thermodynamics and kinetics of electron transfer in the new triads are compared with a previously reported octaalkyldiphenyl-porphyrin triad exhibiting a long-lived spin-polarized charge separate state (CSS), from theoretical and experimental perspectives, in both fluid solution and in a frozen solvent glass. We show that the less favorable oxidation potential of the tetraaryl-porphyrin core can be offset by using C60 , as a better electron-acceptor than triptycenenaphthoquinone (TNQ). The C60 -porphyrin-TAPD triad gives a spin-polarized charge-separated state that can be observed by EPR-spectroscopy, with a mean lifetime of 16 ms at 10 K, which is longer than in the previously reported TNQ-porphyrin-TAPD triad, following the predicted trend from calculated charge-recombination rates.

Rigid triarylamine donor–π–acceptor porphyrin dyes and their application in dye-sensitized solar cells

Three donor–π–acceptor porphyrin dyes bearing the rigid 5-phenyl-carbazole, 5-phenyl-iminodibenzyl and 5-phenyl-iminostilbene donor groups were synthesized and their performance evaluated in TiO2 based dye-sensitized solar cells.

The position effect of electron-deficient quinoxaline moiety in porphyrin based sensitizers

An electron-deficient group, 2,3-diphenylquinoxaline (DPQ), is incorporated as an auxiliary acceptor into the different positions of the porphyrin (Por) based donor-π bridge-acceptor (D-π-A) dye (FNE57) to construct D-A′-Por-π-A (FNE58) and D-Por-A′-π-A (FNE59) configurations. The incorporation of DPQ unit between the donor and porphyrin unit has negligible influence on the absorption property, whereas the DPQ unit located between the porphyrin unit and acceptor significantly increases the absorbance for the Soret band and the valley between the Soret and Q bands. Theoretical calculation reveals that incorporating the DPQ unit adjacent to the acceptor is more advantageous to delocalize the lowest unoccupied molecular orbital and enhance the electronic asymmetry, which facilitates the intramolecular charge transfer. The effect of DPQ unit and its linkage position on the performance of related quasi-solid-state dye-sensitized solar cells (DSSCs) is systematically investigated. The quasi-solid-state DSSC with sensitizer FNE59 displays a power conversion efficiency of 6.02%, which is 23% and 51% higher than those for FNE57 and FNE58 based DSSCs. Our studies facilitate the understanding of the crucial importance of molecular engineering and pave a new path to design novel porphyrin based sensitizers for highly efficient DSSCs.

Synergistic Coupling of Fluorescent “Turn-Off” with Spectral Overlap Modulated FRET for Ratiometric Ag+ Sensor

A useful strategy for ratiometric fluorescent detecting of Ag(+) is demonstrated. Upon selective binding of Ag(+) to a BODIPY-porphyrin dyad (1), the synergistic coupling of two functions, namely the suppressing of FRET from BODIPY donor to porphyrin acceptor and the fluorescence quenching of porphyrin acceptor, leads to exceptionally large changes in the intensity ratio of two distinct emissions (F513/F654) which allow for the ratiometric detecting of Ag(+) with excellent sensitivity in solution and living cells.

Synthesis and characterization of donor-π-acceptor-based porphyrin sensitizers: potential application of dye-sensitized solar cells.

New porphyrin sensitizers based on donor-π-acceptor (D-π-A) approach have been designed, synthesized, characterized by various spectroscopic techniques and their photovoltaic properties explored. N,N'-Diphenylamine acts as donor, the porphyrin is the π-spacer, and either carboxylic acid or cyanoacryclic acid acts as acceptor. All compounds were characterized by using (1)H NMR spectroscopy, ESI-MS, UV-visible emission spectroscopies as well as electrochemical methods. The presence of aromatic groups between porphyrin π-plane and acceptor group push the absorption of both Soret and Q-bands of porphyrin towards the red region. The electrochemical properties suggests that LUMO of these sensitizers above the TiO2 conduction band. Finally, the device was fabricated using liquid redox electrolyte (I(-)/I3(-)) and its efficiency was compared with that of a leading sensitizer.

ChemInform Abstract: Coordination Chemistry‐Assembled Multicomponent Systems Built from a Gable‐Like Bis‐Porphyrin: Synthesis and Photophysical Properties

AbstractReview: 64 refs.

Supramolecular-Surface Photochemistry: Supramolecular Assembly Organized on a Clay Surface Facilitates Energy Transfer between an Encapsulated Donor and a Free Acceptor

We report the occurrence of efficient energy transfer reaction in a novel host–guest assembly composed of an anionic clay nanosheet, cationic porphyrin, and neutral aromatic molecule encapsulated within a cationic organic cavitand. The supramolecular assembly was prepared by the coadsorption of tetracationic Zn–porphyrin (acceptor) and 2-acetylanthracene (donor) enclosed within cationic organic cavitand (octaamine in its protonated form) on anionic clay nanosheets. In this arrangement under the interguest distance of 2.4 nm, almost 100% efficiency of singlet–singlet energy transfer was achieved. Detailed time-resolved fluorescence measurements revealed that the energy transfer rate constant could be attributed to a single component (1.9 × 109 s–1). This strongly suggests that the adsorption distribution of porphyrin and cavitand is rather uniform, not segregated. This is a progress from our previous study that involves energy transfer between two encapsulated neutral molecules. The use of Zn–porphyrin as an energy acceptor in this study enables to connect this energy transfer system to charge separation processes in the same manner as natural photosynthetic systems do; moreover, the efficiency of energy transfer reaction improved to almost 100% from 85% in the previous system between two cavitands.

D-π-A Porphyrin Employing an Indoline Donor Group for High Efficiency Dye-Sensitized Solar Cells

Dye-sensitized solar cell (DSC) devices were fabricated using a novel donor-(π bridge)-acceptor (D-π-A) porphyrin sensitizer, VC-70, in which an indoline is linked directly to the porphyrin core and functions as the donor group. The best efficiencies of VC-70 and reference YD2-o-C8 devices were found to be 7.31 and 7.60%, respectively, and AMG 1.5 illumination and device properties were fully characterized using transient absorption, charge extraction, and transient photovoltage techniques. A notable effect on TiO2 conduction band energetics and electron lifetime was observed following light soaking of VC-70 devices under AMG 1.5 illumination. Upon cosensitization of VC-70 with the organic dye D205 an improved efficiency of 8.10% was obtained.

Coordination Chemistry‐Assembled Multicomponent Systems Built from a Gable‐Like Bis‐Porphyrin: Synthesis and Photophysical Properties

Multiporphyrinic assemblies were quantitatively formed, in one step, from a gable-like zinc(II) bis-porphyrin ZnP2 and free-base porphyrins bearing pyridyl groups. The different fragments are held together by axial 4'-N(pyridyl)-Zn interactions. Formation of a macrocycle ZnP2 •(4'-cisDPyP) and a bis-macrocycle (ZnP2 )2 •(TPyP) is discussed. The macrocycle and the bis-macrocycle were crystallized and studied by X-ray diffraction, which confirmed the excellent complementarity between the various components. Spectrophotometric and spectrofluorimetric titrations and studies reveal high association constants for both multiporphyrinic assemblies due to the almost perfect geometrical match between the interacting units. As expected, energy transfer from the zinc porphyrin component to the free-base porphyrin quenches the fluorescence of the zinc porphyrin components in both compounds. But while in ZnP2 •(4'-cis DPyP) sensitization of the emission of the free-base porphyrin was observed, in (ZnP2)2 •(TPyP) excitation of the peripheral Zn porphyrin units does not lead to quantitative sensitization of the luminescence of the free-base porphyrin acceptor. An unusual HOMO-HOMO electron transfer reaction from ZnP2 to the excited TPyP unit was detected and studied.

Spectroscopy of Donor−π–Acceptor Porphyrins for Dye-Sensitized Solar Cells

A recent improvement in the design of dye-sensitized solar cells has been the combination of light-absorbing, electron-donating, and electron-withdrawing groups within the same sensitizer molecule. This dye architecture has proven to increase the energy conversion efficiency of the cells, leading to record efficiency values. Here we investigate a zinc(II)-porphyrin-based dye with triphenylamine donor groups and carboxyl linkers for the attachment to an oxide acceptor. The unoccupied energy levels of these three moieties are probed selectively by element-sensitive X-ray absorption spectroscopy at the K-edges of nitrogen and carbon. These results are complemented by ultraviolet/visible spectroscopy to obtain the optical band gap and the occupied molecular levels. Density functional theory and time-dependent density functional theory are employed to obtain a detailed understanding of the X-ray and optical absorption spectra. The attachment of electron-donating groups to the porphyrin ring significantly delocalizes the highest occupied molecular orbital (HOMO) of the molecule. This leads to a spatial separation between the HOMO and the lowest unoccupied molecular orbital (LUMO), with the HOMO having significant weight in the amine donors, while the LUMO remains localized in the porphyrin ring and the acceptor group. Such spatial separation of the frontier orbitals reduces the recombination rate of photoinduced electrons and holes, thus enhancing the energy conversion efficiency.

A Ferrocene-Porphyrin Ligand for Multi-Transduction Chemical Sensor Development

5,10,15,20-Tetraferrocenyl porphyrin, H2TFcP, a simple example of a donor-acceptor system, was tested as ligand for the development of a novel multi-transduction chemical sensors aimed at the determination of transition metal ions. The fluorescence energy transfer between ferrocene donor and porphyrin acceptor sub-units was considered. The simultaneously measured optical and potentiometric responses of solvent polymeric membranes based on H2TFcP permitted the detection of lead ions in sample solutions, in the concentration range from 2.7 × 10−7 to 3.0 × 10−3 M. The detection limit of lead determination was 0.27 μM, low enough to perform the direct analysis of Pb2+ in natural waters.

Self-Assembled Nanoscale DNA–Porphyrin Complex for Artificial Light Harvesting

Mimicking green plants' and bacteria's extraordinary ability to absorb a vast number of photons and harness their energy is a longstanding goal in artificial photosynthesis. Resonance energy transfer among donor dyes has been shown to play a crucial role on the overall transfer of energy in the natural systems. Here, we present artificial, self-assembled, light-harvesting complexes consisting of DNA scaffolds, intercalated YO-PRO-1 (YO) donor dyes and a porphyrin acceptor anchored to a lipid bilayer, conceptually mimicking the natural light-harvesting systems. A model system consisting of 39-mer duplex DNA in a linear wire configuration with the porphyrin attached in the middle of the wire is primarily investigated. Utilizing intercalated donor fluorophores to sensitize the excitation of the porphyrin acceptor, we obtain an effective absorption coefficient 12 times larger than for direct excitation of the porphyrin. On the basis of steady-state and time-resolved emission measurements and Markov chain simulations, we show that YO-to-YO resonance energy transfer substantially contributes to the overall flow of energy to the porphyrin. This increase is explained through energy migration along the wire allowing the excited state energy to transfer to positions closer to the porphyrin. The versatility of DNA as a structural material is demonstrated through the construction of a more complex, hexagonal, light-harvesting scaffold yielding further increase in the effective absorption coefficient. Our results show that, by using DNA as a scaffold, we are able to arrange chromophores on a nanometer scale and in this way facilitate the assembly of efficient light-harvesting systems.

Long‐Lived Charge Separation in Novel Axial Donor–Porphyrin–Acceptor Triads Based on Tetrathiafulvalene, Aluminum(III) Porphyrin and Naphthalenediimide

Two self-assembled supramolecular donor-acceptor triads consisting of Al(III) porphyrin (AlPor) with axially bound naphthalenediimide (NDI) as an acceptor and tetrathiafulvalene (TTF) as a secondary donor are reported. In the triads, the NDI and TTF units are attached to Al(III) on opposite faces of the porphyrin, through covalent and coordination bonds, respectively. Fluorescence studies show that the lowest excited singlet state of the porphyrin is quenched through electron transfer to NDI and hole transfer to TTF. In dichloromethane hole transfer to TTF dominates, whereas in benzonitrile (BN) electron transfer to NDI is the main quenching pathway. In the nematic phase of the liquid crystalline solvent 4-(n-pentyl)-4'-cyanobiphenyl (5CB), a spin-polarized transient EPR spectrum that is readily assigned to the weakly coupled radical pair TTF(.+)NDI(.-) is obtained. The initial polarization pattern indicates that the charge separation occurs through the singlet channel and that singlet-triplet mixing occurs in the primary radical pair. At later time the polarization pattern inverts as a result of depopulation of the states with singlet character by recombination to the ground state. The singlet lifetime of TTF(.+)NDI(.-) is estimated to be 200-300 ns, whereas the triplet lifetime in the approximately 350 mT magnetic field of the X-band EPR spectrometer is about 10 μs. In contrast, in dichloromethane and BN the lifetime of the charge separation is <10 ns.

Donor–acceptor porphyrin functionalized Pt nano-assemblies for artificial photosynthesis: a simple and efficient homogeneous photocatalytic hydrogen production system

In this paper, a novel porphyrin dye (5,10,15,20-tetrakis (4-(anthracene-1-ylmethoxy)phenyl) porphyrin, TPPAN) and its functionalized platinum nanoparticles (Pt-TPPAN) were synthesized. Using the Pt-TPPAN nanocomposite as a photocatalyst, a new and more compact photoinduced hydrogen evolution system from an aqueous ethanol solution without additives was developed. Fluorescence and photo-electrochemical spectra reveal that photoinduced electron transfer occurs from the photoexcited state of anthracene substituents to the porphyrin, accompanied by an electron transfer from the excited porphyrin moiety to the Pt co-catalyst. The photocatalytic activity results suggested that this TPPAN functionalized Pt nano-assembly could efficiently catalyze hydrogen evolution from an aqueous ethanol solution under simulated solar light irradiation. Therein, the TPPAN molecule in the nanocomposite worked as a light absorption antenna and the nanocore Pt species acted as a co-catalyst. This investigation might offer a new paradigm for constructing a simpler and more efficient homogeneous photocatalytic hydrogen evolution system for mimicking natural photosynthesis.

Enhanced performance of solution-processed solar cells based on porphyrin small molecules with a diketopyrrolopyrrole acceptor unit and a pyridine additive

A conjugated donor–acceptor porphyrin small molecule was designed and synthesized with diketopyrrolopyrrole as the acceptor unit. The new porphyrin-based small molecule exhibits broad and intense absorption in the visible and near IR regions, and the hole mobility and the power conversion efficiency of the bulk heterojunction devices based on the porphyrin : [6,6]-phenyl-C-61-butyric acid methyl ester (1 : 1, w/w) are increased up to 4.6 × 10−5 cm2 V−1 s−1 and 3.71%, respectively, which are further enhanced to 1.6 × 10−4 cm2 V−1 s−1 and 4.78%, respectively, upon the introduction of 3.0 vol% of pyridine additive. Further studies show that the performance of the solar cells based on other zinc porphyrins could also be improved by the pyridine additive.

Hierarchical Self-Assembly of a Biomimetic Light-Harvesting Antenna Based on DNA G-Quadruplexes

A new modular approach to an artificial light-harvesting antenna system is presented. The approach involves the hierarchical self-assembly of porphyrin acceptor molecules to G-quadruplexes tethered to coumarin donor moieties.

Novel zinc porphyrin sensitizers for dye-sensitized solar cells: Synthesis and spectral, electrochemical, and photovoltaic properties

Two donor–π-spacer–acceptor porphyrin dyes were synthesized for use in dye-sensitized solar cells. The dyes comprised the same donor (porphyrin derivative) consisting of 3,4,5-trimethoxybenzaldehyde and acceptor/anchoring group (carboxyl group) but varying π-spacer consisting of a Schiff base structure. Each of the dyes displayed different adsorption behavior and coverage on the TiO2 surface. The porphyrin dyes PZnBIACOOH studied in this work exhibit red-shifted and broadened electronic spectra respect to the reference PZnCOOH as expected. By the introduction of Schiff base unit at the meso positions, the energy level of Eox (excited-state oxidation potentials) is significantly shifted to the positive compared with the reference PZnCOOH, indicating a decreased HOMO–LUMO gap. The highest power conversion efficiency of the two dyes based on DSSCs reached 1.75% under AM 1.5 G irradiation.

Energy Transfer and Concentration-Dependent Conformational Modulation: A Porphyrin-Containing [3]Rotaxane

A zinc porphyrin-containing [3]rotaxane A was synthesized through a copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. Energy donors and acceptor porphyrin were introduced to dibenzo[24]crown-8 (DB24C8) and dibenzyl ammonium (DBA) units of [3]rotaxane A to understand the intramolecular energy transfer process. Investigations of the photophysical properties of [3]rotaxane A demonstrated that the intramolecular efficient energy transfer readily occurred from the donors on the wheels to the porphyrin center on the axis. The fluorescence of energy donors in the region of 400 to 450 nm was efficiently absorbed by the porphyrin acceptor under irradiation at 345 nm, and finally a red light emission at about 600 nm was achieved. Further investigation indicated that the conformation of [3]rotaxane A was self-modulated by changing its concentration in CH(2)Cl(2). The triazole groups on the wheel coordinated or uncoordinated to Zn(2+) through intramolecular self-coordination with the change in the concentration of [3]rotaxane A in CH(2)Cl(2). Therefore, this conformational change was reversible in a non-coordinating solvent such as CH(2)Cl(2) but inhibited in a coordinating solvent such as THF. Such interesting behaviors were rarely observed in porphyrin derivatives. This self-modulation feature opens up the possibility of controlling molecular conformation by varying concentration.